1. Field of the Invention
The present invention concerns a double conversion tuner for a television receiver with provisions for altering the frequencies of the carriers of the first intermediate frequency signal to change their amplitudes or phases.
2. Description of Related Art
From the earliest days of television, it has been known to purposely "misfine tune" a receiver so that the frequencies of carriers in the passband of the IF filter are shifted or offset from their nominal frequencies to change the amplitude of the carriers and thereby subjectively enhance the receivers' video and audio responses. However, because traps and other frequency selective networks, such as those associated with a synchronous demodulator, are set assuming the carriers of the IF signal are at nominal frequencies, misfine tuning the receiver is not particularly desirable.
Rather than controlling the frequencies of the IF carriers, it has also been proposed to control the shape (or "tilt") of the amplitude versus frequency response characteristics of the IF filter section of a television receiver to control the amplitudes of the carriers for various purposes. Among these purposes are compensation for the non-linear amplitude versus frequency response characteristic of the antenna and RF filter section of the television receiver (see U.S. Pat. No. 4,366,498--Theriault), automatic chroma control (see U.S. Pat. Nos. 3,079,461--Keizer, and 2,921,120--Pritchard et al.) and adjustment of the ratio of the luminance and chrominance signals (see U.S. Pat. Nos. 2,934,599--Holmes, and 4,366,498--Theriault). Such prior IF tilt arrangements typically have included variable reactive components such as a varactor diode which add cost and complexity to the IF filter section.